NFPA 1903: MOBILE WATER SUPPLY APPARATUS
VOLUNTEERS CORNER
The NFPA Fire Department Equipment Committee has developed a new 1991 standard to address mobile water supply apparatus—NFPA 1903. This standard has its base in the former NFPA 1901, Automotive Fire Apparatus. The scope of the 1903 standard covers new fire apparatus designed for the transport of water to the scene of an emergency.
Mobile water supply apparatus are commonly referred to as “tankers”; however, in ICS clear text they are designated “tenders.” They are also to be distinguished from pumper-tankers, which carry all necessary equipment for structural firefighting. Pumper-tankers must follow NFPA 1901, Pumper Fire Apparatus, since they function as pumpers but have enlarged water tanks.
Since a mobile water supply apparatus is designed to transport water, there are some important tank requirements. The tank size must be a minimum of 1,000 gallons. There is no maximum as long as the chassis weight limitations are not exceeded and road tests can be met. The tank must be constructed (baffling and venting) to load from an external source at a flow rate of 1,000 gallons per minute with a connection directly to the tank. The tank also must be capable of unloading at a flow rate of 1,000 gpm. A single outlet is required but must be fitted with piping, a chute, flexible hose, or an L-shaped pipe so water can be delivered to either side or the rear of the vehicle. Multiple outlets are acceptable.
Two considerations about the water tank that are not in the standard are usable water and jet-assisted unloading. The tank size is the nominal (theoretical) capacity, which may differ from the actual amount of usable water. If the nominal capacity is the amount of usable water required, it should be specified, and a larger tank may be necessary. ISO, when rating these vehicles, anticipates 90 percent of the nominal tank capacity as usable water. Normally the flow’ rate for unloading the tank can be sustained for only 80 to 90 percent of the tank capacity. Below that a reduced flow’ rate should be anticipated. However, tanks equipped with an unloading trough that runs under the entire length of the tank can exceed this percentage. A jet-assisted tank discharge (dump) will increase the offloading rate. Piping the pump-to-tank fill line to the throat of the external tank discharge can create a jet assist. If a jet-assisted discharge is desired, it must be specified.
Mobile water supply apparatus are not required to have a pump, but if a pump is requested, any size is acceptable. Depending on the operations of the department, a transfer pump (mounted or portable pump with a minimum capacity of 250 gpm at 50 psi), an attack pump (mounted pump with a capacity of 250 to 700 gpm), or a fire pump (mounted pump with a capacity above 750 gpm) may be desired. The standard has a chapter with the requirements for each type of pump. The inclusion of a pump will add versatility to a mobile water supply apparatus. With a pump the unit will have fire suppression capability; possibly pump-and-roll operation; the ability to pump off the tank; and, if plumbed accordingly, a jet assist to aid in unloading.
The standard addresses several aspects of firefighter safety. Among them are fully enclosed riding compartments with seats and seat belts for each firefighter; flush door handles; nonslip grab rails; nonslip access steps and platforms; larger and stronger steps; cab noise levels; intersection lights; work area, step, and walkway lighting; and reflective stripping requirements. No audible warning devices are permitted on the cab roof. The first step can be a maximum of 24 inches from the ground, and all others a maximum of 18 inches in height; they must be 35 square inches and support 500 pounds,
A minimum of 18 cubic feet of equipment and tool storage eompartmentation must be provided. Hose storage requirements are less than those for pumping apparatus. They are minimum requirements and may have to be adjusted to suit departmental SOPs and pump capacities. One securely mounted SCBA with a spare bottle is required for each seat. Since the vehicle’s purpose is to transport water, a minimum amount of equipment is required. A 1,500-gallon minimum portable tank is required. Equipment carried should be specified to meet departmental operational needs. Although not required, consider carrying a low-level suction device; also consider jet-siphon devices if multiple portable tanks will be used in a shuttle operation.
Although not required by the standard, 1 highly recommend diesel engines, automatic transmissions, air brakes with antilock braking systems, and automatic transmissions (unless specifically excluded). With antilock braking, another option is antispin reduction or traction control that controls spinning during acceleration. The larger the water tank size and weight of the truck, the more vital these items become. If the unit is underpowered, overloaded, or underbraked, it cannot travel safely and should not be on the road. If performance counts, put it in the specifications. A performance specification is more valuable than a design specification; let the engineers do the design.
Design your mobile water supply apparatus around the chassis that you intend to use. Don’t overspecify or underspecify the unit. By all means, avoid getting the wrong gvw-rated chassis—there is a strong tendency to increase the tank size and overload the chassis. Remember that modifications to four-door cabs, additional equipment placed on the unit after delivery (that was not planned), and items like four-wheel drive conversions all add weight. The extra weight often leads to a problem of insufficient drive line components including engine capability, transmission size, and braking ability.
Then there are suspension and axle difficulties. Make sure the tires match the intended vehicle use and components.
Another major area of concern is the electrical system. Be sure all system components are large enough to handle the planned usage. The electrical portion of your specifications must be well thought out and developed to avoid problems later.
As you initiate the purchase of a new mobile water supply apparatus and prepare to write specifications, obtain a copy of the new 1991 edition of NFFA 1903. Study it carefully, and then develop your specifications around it to obtain the unit you need for your community’s fire protection challenges.
